Things we have learned (1)

Hydrology of the Severn

The regulation of the Severn’s water is complex, involving two reservoirs and groundwater extraction to supplement the flow. A study of the monthly average flow rates monitored at the Bewdley gauging station reveal the variations in flow, and thus level of the river throughout each year. Records from 1923 were studied, so we have nearly 90 years to compare. Highest flows can occur any month between Sept and March – and lowest monthly averages can occur any month between April and October – though more often June, July or August sees the lowest flows. Flows well below the agreed ‘minimum flow’ guaranteed by the use of the Clywedog reservoir are recorded, and conversely the high rates leading to flooding can also be seen – even more erratic in recent years! In spite of the statements made at the time of the opening of the Clywedog system, it is clear that, overall the reservoir has enabled greater abstraction, whilst not particularly alleviating flood risk. Nor for that matter does the system protect against very low levels and consequent loss of fish stocks.